Constant current pulse generator



Jan. 10, 1967 wj 3,297,954

CONSTANT CURRENT PULSE GENERATOR Filed Aug. 25, 1964 2 Sfieets-Sheet 1 Ii-E TRJG

U 1 01 TI TFZIG IN VENTOR. (Ha/Fame 6/2255 Huey Jan. 10, 1967 w|LEY 3,297,954

CONSTANT CURRENT PULSE GENERATOR Filed Aug. 25, 1964' 2 Sheets-Sheet 2 l l .i

IN VENTOR. i/wei/wf 62:55 MLE BY United States Patent 3,297,954 CONSTANT CURRENT PULSE GENERATOR Lawrence Grebe Wiley, Camp Hill, Pa., assignor to AMP Incorporated, Harrisburg, Pa. Filed Aug. 25, 1964, Ser. No. 391,933 3 Claims. (Cl. 331-52) This invention relates to a simplified pulse generator circuit.

It is one object of the invention to provide a pulse generator which has fewer and less expensive circuit components than heretofore available.

It is a further object to provide a pulse generator adapted to supply a constant current pulse drive for a varying impedance load.

It is yet another object of the invention to provide a stable and reliable pulse generator having a simple constant current regulating means incorporated therein.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there are shown and described illustrative embodiments of the invention; it is to be understood, however, that these embodiments are not intended to be exhaustive nor limiting of the invention, but are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.

The foregoing objectives are attained by the invention through a circuit having square pulse producing oscillators adapted to drive an output transformer through a constant current means adapted to maintain the current from each oscillator constant, notwithstanding variations in a load tied to the transformer secondary or in the circuit supply.

In the drawings:

FIGURE 1 is a schematic diagram showing the circuit of the invention and the components thereof in block form; and

FIGURE 2 is a schematic diagram showing in detail a specific embodiment of the circuit of the invention.

In FIGURE 1 a load Z shown as element 32 is adapted to be driven through lead 30 from the secondary of a transformer T The load may be considered as of .the type which varies substantially. Although the circuit of the invention is not limited to such applications, for the purpose of clarity of description the load may be considered as a string of multiaperture cores threaded by a winding connected to 30 in a manner where the output of the circuit of the invention supplies an RF drive to switch the core material and thereby produce an output which is a measure of the binary intelligence pattern within such cores. With arrangements of this type the impedance seen by the windings threading the cores will vary in accordance with the intelligence pattern in the cores, which, of course, varies with the one-zero content of the core device. In an application of the circuit of the invention the requirements for driving a string of twenty magnetic cores were defined as providing a supply of approximately 300 kilocycles, square wave pulses of 250 milliamperes peak-to-peak amplitude, with a current variation not exceeding ten percent. As one further requirement and as a general rule for commercial circuits, the circuit providing such drive should be adapted for use with a standard voltage source such as the 24 volt supply widely employed in electronic equipment.

Thus, with respect to the circuit of FIGURE 1 a standard voltage supply B is indicated as at lead 12 3,297,954 Patented Jan. 10, 1967 supplying in parallel via leads 16 and 18, oscillators denominated O and 0 having the outputs thereof tied to the primary of a transformer T The oscillators have a further connection schematically indicated, such upon the cessation of the output pulse from a given oscillator a trigger pulse is provided to the adjacent oscillator to initiate conduction thereof to produce its pulse. The oscillators O and are of the transformer-coupled type wherein when the circuit is first turned on and a voltage is applied one of the oscillators will turn on first, the other oscillator being held off. The oscillator which is turned on will regeneratively build up to provide a sharply rising output current which will, as the transformer material saturates, suddenly cut off to provide a sharply falling output current to zero, the fall off being also regenerative. Each oscillator thus produces a half cycle before oscillation is halted and the circuit is such as to prevent a subsequent unblocking without the aid of an externally supplied trigger, i.e., from the adjacent oscillator. The rise and fall of current thus provided is in conjunction with the circuit parameters chosen such as to make the pulse substantially square in shape and the transformer resonance is such as to provide a proper duration for such pulse. With this arrangement the leads 22 and 24, representative of output leads for the oscillators, provide a pulse wave form seen by the primary of tranformer T as alternate square wave pulses of opposite phase. A center tap on the transformer provides a path for such pulses, shown via lead 26 to a constant current device CD and lead 28 to ground. With this circuit then, the current level experienced by each half of the primary of transformer T is regulated directly by the operation of CD.

The device 26 thus serves to regulate both of the oscillators O and O and to provide regulation for a generator which inherently is altering its current output to provide square wave pulses.

The application advantages of the circuit of FIGURE 1 embrace both the accommodation of variations in Z and in the voltage supply E which may be expected to vary somewhat above and and below its standard rating. Considering a voltage drop with regard to E the oscillators O and 0 would thus be expected to drop the current level of the pulses supplied. The constant current device CD, however, operates to hold such current constant and the only basic requirement is. that there be just enough voltage E to operate 0 and O and 26 along with the impedance of the connecting circuitry including the maximum impedance of Z;,. An elevation of B is controlled in a similar manner with 26 acting to hold the current level of the output pulses constant.

FIGURE 2 shows a preferred embodiment of the invention employing all solid state components. From the power supply E lead 12 is connected to provide a supply to oscillators 0 0 via leads 16 and 18 through the primary of cross coupling transformer T a capacitor C which as as a low impedance pulse suppressor, and to the constant current device CD via a lead 14. Lead 14 includes a connection to a lead 20, which includes a resistor R utilized to develop a starting voltage for 0 Each of the oscillators is substantially the same to include in the preferred embodiment, referring to 0 a pair of NPN transistors, Q and Q having the collectors thereof in parallel with respect to lead 16 and the primary of T The base of each of the transistors Q and Q is tied in parallel via lead 22 through a resistor R to the secondary of T and at the other end of such transformer to the emitter of Q and Q through resistors R and R The resistor R serves to limit the current to the base of each of the transistors and the resistors R and R serve to apply an appropriate voltage between the emitters and base of each transistor across the secondary of the transformer. The oscillator is substantially identical to include NPN transistors Q and Q resistances R R and R having substantially the same function and tied to a secondary of the transformer T in the same manner through a lead 24 and to the primary thereof through lead 18. The primaries and secondaries of transformer T are wound upon the same magnetic core and essentially operate as a voltage step-up transformer to drive the collectors of the transistors of O and O and provide a linkage between the bases of such through the linkage in the magnetic material of such core.

The outputs of oscillators O and 0 are in parallel through the primary of transformer T to provide an output to a secondary winding of T connected across load Z The secondary of T is essentially a step-up transformer and is linked through a common magnetic core to the individual primary windings tied to the outputs of O and O The lead 26 connects the primaries of transformer T to the collector of a NPN transistor Q in the constant current device CD. The base of Q is tied via lead 14 through a current limiting resistor R to E and the emitter of Q is tied to ground via lead 28 through resistor R, which serves to establish an appropriate drop between the base and emitter electrodes of Q Across this same path via lead 31 is a zener diode Z In operation, upon the application of E to lead 12, the path via lead across resistor R will develop a voltage on the base of Q and Q to cause such to conduct, drawing current through the half of the primary of T associated with the collector electrodes thereof and in turn causing current in the secondary to develop a regenerative action which reverses to drop the flow of current in the transistor circuits upon the core of T becoming magnetized. The oscillator 0 then produces a square wave half cycle output to the associated half of the primary of T such flowing through the center tap connection via 26 to Q and resistor R to ground via lead 28. This pulse induces a voltage in the secondary of T which causes a current to flow through load Z The wave shape thus produced is shown as the first half cycle in FIGURE 1. The fall of the current output from O develops a collapsing field in the core of T; which is common to O to apply voltage drop via resistor R and gate the transistors Q and Q on. A similar regenerative action then occurs to provide a fast rise time pulse having an on time tied to the resonance of the circuit including the secondary and a fast fall time pulse to produce an output pulse on the other half of the primary of T flowing through Q and R to ground. This produces a pulse output substantially the same as that of the first phase but of opposite polarity. A full cycle square wave pulse is thus applied to the lead 30 through the secondary of transformer T with the current of both half cycles being drawn through CD.

During this operation the zener Z operates to control the voltage applied across the base of Q and the emitter including R Assuming now that there is a change in Z which will reflect a potential difference into the primary T to either raise or lower the potential across R Z will then operate depending upon whether the potential is dropped below or above its rating to tend to cut off Q; as the base thereof swings negative or hold such on at a constant current. The device CD stabilizes to draw a constant current notwithstanding the potential difference reflected into the primary of T by changes in Z In the same manner changes in E within normal variation of supply voltage are not permitted to alter the current output of the oscillators through the primary of T because CD maintains a constant current, the voltage changes not affecting the current being drawn by CD. As to the circuit of FIGURE 2, the energy requirements thereof in conjunction with the maximum power required by the load are made, relative to the available power supply, such that with any expected variation there is always suflicient energy for operating the device.

The use of two NPN transistors per oscillator stage is for the purpose of achieving economy, by employing two relatively low-cost low power units rather than a single high cost unit of a greater power capacity. It is to be understood that a single transistor can be employed or that PNP or other devices having substantially the same function could be employed with an appropriate change in polarity of drive.

In an actual unit constructed in accordance with the referred mode of the invention the circuit of the invention included the following components:

Q Q RCA 2N2270 NPN transistor Q RCA 2N1701 NPN transistor T was wound on an Arnold Inc. No. A051027-2 Core with ten turns on each side of the primary and 50 turns on each side of the secondary.

T was wound on an Arnold Inc. No. A-204091-2 core with 75 turns on each primary and 225 turns on the secondary.

Z was a Motorola Inc. No. 1N821 zener diode C -10 microfarads, 35 volt R 3.3K ohms, /2 watt R 100 ohms, watt R R R and Rq22 ohms, 1 watt R -1.8K ohms, /2 watt R 18 ohms, 3 watts This device was operated by a power supply E :24:2 volts to drive a load ranging from approximately 24 ohms to 148 ohms.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by Way of illustration only.

What is claimed is:

1. A pulse generator circuit of the type utilized to sup ply a load, said generator circuit including a pair of oscillators each having a regenerative action and connected to alternately produce a substantially square-wave pulse of a half cycle, as the output of each separate oscillator, a transformer having a primary winding tapped in the center thereof and a secondary winding connected to a load, the outputs of the oscillators being separately applied to different ends of said primary winding of said transformer to develop a series of square-wave pulses of opposite polarity in said secondary winding to drive said load, a ground for said circuit, means connected to the primary winding center tap and to said ground to hold the said square-wave pulse output of each of said oscillators at a constant current level drawn through the said primary winding when said oscillators are conducting whereby to provide a square-wave pulse output of constant current level to the said secondary winding and to said load.

2. A pulse generator circuit for supplying a constant current to a load having a varying impedance including a pair of oscillators each operable during conduction to produce a half cycle output having a substantially square-wave pulse form, means connected to said oscillators including a first transformer operable upon cut off of a given oscillator to provide a trigger pulse to the other oscillator to trigger such to its on condition, a second transformer having a primary winding and a secondary winding, the outputs of each said oscillator being con nected in an opposite sense to the primary winding of said second transformer, the secondary winding of the second transformer being connected to a load to provide cycles of pulses of alternating polarity thereto, the primary winding of said second transformer being connected to a constant current device, including means sensitive to increases or decreases relative to a fixed voltage to hold the current drawn thereby and through said second transformer primary Winding from said oscillators at a constant value, notwithstanding reflected potential differences from changes in impedances in said load impressed upon the secondary winding of said second transformer.

3. A constant current pulse generator circuit for supplying square-wave pulses to a load, said circuit comprising a supply voltage and a pair of oscillators crosscoupled to supply triggers to each other, said oscillators being of the regenerative type to each provide a substantially square-wave pulse output of a half cycle, an output transformer connected to the output of said oscillators, the said output transformer having a primary Winding and a secondary winding with the secondary winding being connected to supply drive pulses to the load, the said primary winding being tapped in the center thereof and each of the outputs of the said oscillators being separately applied to different ends of said primary winding of said transformer to develop a series of square-wave pulses of opposite polarity in said secondary winding to drive said load, a ground for said circuit, constant cutrent means connected between the primary winding center tap and said ground to hold the said square-wave pulse output of each of said oscillators at a constant current level drawn through the said primary winding when said oscillators are conducting whereby to provide a squarewave pulse output of constant current level to said secondary winding and to said load notwithstanding potential differences reflected from changes in impedance in said load or from variations in said supply voltage.

References Cited by the Examiner UNITED STATES PATENTS 2,708,241 5/1955 Bess 331-146 X 2,977,550 3/1961 Roesel et al 331-112 X 2,999,170 9/1961 Tyler 331-56 X 3.114,872 12/1963 Allard 307-885 3,144,581 8/1964 Greenburg et al. 33l-112X 3,222,616 12/1965 Harriger 331-113 ARTHUR GAUSS, Primary Examiner. I. ZAZWORSKY, Assistant Examiner. 

1. A PULSE GENERATOR CIRCUIT OF THE TYPE UTILIZED TO SUPPLY A LOAD, SAID GENERATOR CIRCUIT INCLUDING A PAIR OF OSCILLATORS EACH HAVING A REGENERATIVE ACTION AND CONNECTED TO ALTERNATELY PRODUCE A SUBSTANTIALLY SQUARE-WAVE PULSE OF A HALF CYCLE, AS THE OUTPUT OF EACH SEPARATE OSCILLATOR, A TRANSFORMER HAVING A PRIMARY WINDING TAPPED IN THE CENTER THEREOF AND A SECONDARY WINDING CONNECTED TO A LOAD, THE OUTPUTS OF THE OSCILLATORS BEING SEPARATELY APPLIED TO DIFFERENT ENDS OF SAID PRIMARY WINDING OF SAID TRANSFORMER TO DEVELOP A SERIES OF SQUARE-WAVE PULSES OF OPPOSITE POLARITY IN SAID SECONDARY WINDING TO DRIVE SAID LOAD, A GROUND FOR SAID CIRCUIT, MEANS CONNECTED TO THE PRIMARY WINDING CENTER TAP AND TO SAID GROUND TO HOLD THE SAID SQUARE-WAVE PULSE OUTPUT OF EACH OF SAID OSCILLATORS AT A CONSTANT CURRENT LEVEL DRAWN THROUGH THE SAID PRIMARY WINDING WHEN SAID OSCILLATORS ARE CONDUCTING WHEREBY TO PROVIDE A SQUARE-WAVE PULSE OUTPUT OF CONSTANT CURRENT LEVEL TO THE SAID SECONDARY WINDING AND TO SAID LOAD. 